The present invention relates to a method of polishing at least one surface of a silicon-based part made of silica, SiC, glass, quartz, or indeed a vitro-ceramic.
Polishing methods are already known which implement a pre-polishing stage by means of at least one polishing element, e.g. a cast iron plate, and an abrasive, e.g. emery, so as to confer a xe2x80x9ccoarsexe2x80x9d first roughness to the surface, followed by a stage of polishing proper that implements at least one polishing element, e.g. a polyurethane support or pitch, and a liquid containing an abrasive, and in particular an abrasive oxide, e.g. an oxide of cerium or of zirconium, to confer a second roughness to said surface that is smaller, i.e. finer, than said first roughness.
Such methods enable highly polished surfaces to be obtained in which the second roughness is smaller than 10 xc3x85, and is of the order of a few xc3x85.
Nevertheless, the Applicant has observed that in spite of that high quality surface state, parts made using those known methods present flux strength that is not satisfactory.
Flux strength represents the quantity of energy that a surface can receive without shattering. It can be measured by means of a pulsed laser that emits pulses of given wavelength and duration. It is then expressed in J/cm2. It is expressed in W/cm2 for continuous lasers.
The present invention is based on the idea that the unsatisfactory flux strength of such a silicon-based part which has been polished by known methods is due in particular to the surface being contaminated by residues of exogenous abrasive (e.g. cerium oxide or zirconium oxide) remaining after polishing. In addition, the surfaces obtained by known methods are also liable to present microcracks which also decrease flux strength.
An object of the invention is to improve the flux strength of the surface of such a silicon-based part, and to this end, the invention present, after pre-polishing and polishing stages, a finishing stage by soft abrasion implementing at least one finishing element, in particular a felt, and a soft abrasive constituted in particular by colloidal silica, so as to remove a surface layer of sufficient thickness to improve the flux strength of said part.
During this step, roughness is not necessarily improved, in particular for parts where an improvement in flux strength is specifically desired, e.g. silica parts for power lasers. Nevertheless, it should be observed that the method of the invention makes it possible, if necessary, to obtain improved roughness that can be of the order of 1 xc3x85.
When the part is a plane part, the method is preferably implemented by polishing two opposite parallel plane faces of said plane part simultaneously, even if a high quality surface state is required for only one of the faces of the part.